THESE SEEM like boom times in Montgomery County, the mainly rich suburb that has absorbed roughly 100,000 new residents since 2010 to a population now approaching 1.1 million. Amazon (whose CEO, Jeffrey P. Bezos, owns The Post) has shortlisted the county for its second corporate headquarters; construction cranes tower over Bethesda and Silver Spring; and the public school system, one of the nation’s largest, includes some of the best high schools anywhere.

That’s why it’s easy to overlook some ominous signs of fiscal and economic trouble ahead. A burgeoning population of retirees, immigrants and other less affluent residents has strained local resources and budgets. Those moving into the county tend to be poorer than those leaving. The chasm between economically prosperous pockets (such as the ones dominated by cranes) and stagnant ones is widening. Most worrying, business and job growth are anemic.

That’s the unsettling backdrop for the June 26 Democratic primary, which is likely to determine who will run the county for the next four years. County Executive Isiah Leggett, a deft and capable manager, is retiring after 12 years in the job (and no Republican has won an election in Montgomery since 2002). The central question is which of the candidates for county executive is most capable of juicing a sluggish commercial environment — the only way to broaden the local tax base so it can sustain the county’s excellent schools and progressive services.

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We think the best bet is David Blair, a dynamic political newcomer with business acumen, energy and passion for innovation.

Mr. Blair, who started and sold a successful prescription-drug benefits company, is a political outsider but a lifelong Montgomery resident, and with an insider’s appetite for policy detail, budget numbers and rigorous analysis. His entrance to a race that includes three sitting (but term-limited) County Council members, a former mayor and an incumbent state legislator was greeted with some derision. Since then he has changed minds. Yes, his outsize campaign spending and squadrons of paid door-knockers have helped with that. But so have his eagerness to listen and his substantive but realistic ideas for attracting new business, extending pre-K, preparing young people for the workforce and improving traffic.

Granted, Mr. Blair would face a learning curve in office. At 48, he is a generation younger than his chief rivals, who are steeped in Montgomery politics and veterans of countless policy battles. They include Rose Krasnow, a knowledgeable former mayor of Rockville who spent 13 years as a top county planner; Roger Berliner and George Leventhal, accomplished lawmakers on the County Council; and another long-serving council member, Marc Elrich, whose popularity owes much to his reflexive opposition to innumerable local projects — including the Fillmore, a beloved live music venue in Silver Spring. Mr. Elrich would be the wrong person to broaden the county’s tax base and revive its prospects. Those candidates, as well as another, state Del. Bill Frick, are smart and substantive.

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Mr. Blair would make an unorthodox county executive. With his combination of fresh thinking and business savvy, he would also stand the best chance of injecting a dose of vitality into a county that badly needs it.